K2-72e (also known by its EPIC designation ''EPIC 206209135.04''), is a confirmed

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

, likely rocky, orbiting within the

habitable zone In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kas ...

of the

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

K2-72 K2-72 (also designated EPIC 206209135) is a cool red dwarf star of spectral class M2.7V located about away from the Earth in the constellation of Aquarius. It is known to host four planets, all similar in size to Earth, with one of them re ...

, the outermost of four such planets discovered in the system by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

's ''

Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...

'' spacecraft on its "Second Light" mission. It is located about 217.1

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s (66.56

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s, or nearly km) away from Earth in the constellation of

Aquarius Aquarius may refer to: Astrology * Aquarius (astrology), an astrological sign * Age of Aquarius, a time period in the cycle of astrological ages Astronomy * Aquarius (constellation) * Aquarius in Chinese astronomy Arts and entertainme ...

. The exoplanet was found by using the

transit method Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty o ...

, in which the dimming effect that a planet causes as it crosses in front of its star is measured.

Characteristics

Mass, radius, and temperature

K2-72e is an Earth-sized exoplanet, meaning it has a mass and radius close to that of Earth. It has an equilibrium temperature of . It has a radius of 1.29 ., and a mass of 2.2 , depending on its composition.Orbit graphic with a table of simplified figures
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Host star

The planet orbits a ( M-type)

named

, orbited by a total of four planets, of which K2-72e has the longest orbital period. The star has a mass of 0.27 and a radius of 0.33 . It has a temperature of 3360 K and its age is unknown. In comparison, the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

is 4.6 billion years old and has a surface temperature of 5778 K. The star's

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

, or how bright it appears from Earth's perspective, is 15.309. Therefore, it is too dim to be seen with the naked eye and can only be observed with a telescope.

Orbit

K2-72e orbits its host star with an orbital period of 24 days and an orbital radius of about 0.1 times that of Earth's (compared to the distance of

Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

from the Sun, which is about 0.38 AU).

Habitability

The exoplanet, along with K2-72c, were announced to be orbiting in the habitable zone of its parent star, the region where, with the correct conditions and atmospheric properties, liquid water may exist on the surface of the planet. K2-72e has a radius of 1.29 , so it is likely rocky. Its host star is a

, with about a fifth as much mass than the Sun does. As a result, stars like K2-72 have the ability to live up to 1–2 trillion years, hundreds of times longer than the Sun will live. The planet is very likely tidally locked, with one side of its hemisphere permanently facing towards the star, while the opposite side shrouded in eternal darkness. It receives 11% more insolation than Earth does, so any oceans present are potentially vulnerable to boiling away, therefore possibly reducing the chance of habitability.

Discovery

The planet, along with the other three planets in the K2-72 system, were announced in mid-July 2016 as part of the new results from the second mission of the

spacecraft.

References

{{DEFAULTSORT:K2-72e Exoplanets discovered in 2016 Exoplanets in the habitable zone Transiting exoplanets Near-Earth-sized exoplanets in the habitable zone Aquarius (constellation) 72